1. Field of the Invention
The invention relates to a calibration process of at least one sensor of a wind power plant and a corresponding wind power plant.
2. Description of Related Art
Due to the continuously growing size of rotors of wind power plants, control strategies for the minimization of loads on the wind power plant, in particular a control strategy for a blade revolution pitch, continue to gain in importance. For example, each rotor blade is hereby individually turned into the wind (pitched) during the revolution so that the total mechanical load, which is conveyed into the tower via the rotor shaft and the nacelle, can be minimized. As an important measurement variable, blade bending moments are hereby required for each rotor blade or other bending moments of the wind power plant, for example on a generator shaft or the rotor hub or other rotating parts. Corresponding load measurements are also required by corresponding sensors for load measurements of the wind power plant.
Sensors can hereby not be attached one hundred percent exactly at the location where they should be attached, and the sensor properties can change over time so that a calibration of the sensors is necessary, which is normally performed manually. The load on the rotor blade root in modern wind power plants is mainly characterized by a superimposition of the bending moments from aerodynamics (mainly perpendicular to the rotor plane, according to the impact moment) and the bending moment, which from the tare weight of the rotor blades, mainly in the rotor plane (swing moment) and normal forces resulting from the tare weight and the centrifugal force (depending on the rotor speed) and forces and moments from the dynamic of the rotors, which are of particular importance when there are undesired vibrations (see DE 102 19 664 A1).
In order to perform load measurements, strain gauges are normally used, which are normally connected such that only bending strains, but not normal forces from temperature strains or centrifugal forces, are taken into consideration. The calibration of the blade root bending moments takes place against the gravity bending moment from the known mass and the known center of gravity distance of the blade from the measurement point when the rotor blade is placed horizontal. In order to determine the zero point of the bending moment measurements, the rotor blade is set vertically or, alternatively, horizontally, wherein the rotor blade is rotated around the rotor blade longitudinal axis (pitched) in order to determine the zero point for the horizontal positioning. The impact or swing bending moment is accessible by rotating the blade pitch angle by 90°, which the selected calibration method can easily do. Thus, for selection and calibration, the system must be shut down for a short period of time according to the article entitled “Messung von Lastkollektiven in einem Windpark” (Measurement of Load Collectives in a Wind Farm) by H. Seifert and H. Söker in DEWI, 1994, pages 399 through 402. For this, the data is output via a notebook and evaluated accordingly in order to perform a calibration.